SARS-CoV-2 with various reported variants has infected more than 216 million people worldwide with clinical symptoms from asymptomatic, mild, moderate, and severe. SARS-CoV-2 detection becomes very important to evaluate the spread of the virus in the community. The gold standard of SARS CoV-2 detection is viral nucleic acid using real-time RT-PCR. The most frequently used is the real-time qualitative PCR test. For a better understanding of COVID-19 pathogenesis, a quantitative assay to measure viral load is necessary. To meet this need, a viral load assay was developed using RNA standard transcribed in vitro. In addition, we evaluated the sensitivity and specificity of this assay using clinical specimens from Jakarta, Indonesia. The target of this assay was nucleocapsid gene (N) SARS CoV-2 and human protein gene RNase P (RP) as internal control, respectively. The specimens were taken from 44 patients with clinical symptoms of COVID-19 on the first day of presentation in Sari Asih Hospital, Jakarta, from June-November 2021. In comparison with CDC’s primers and probes as a gold standard in Indonesia, the sensitivity and specificity of this assay was 100% with limit of detection 6,5 copy number/µL. In our study, there was no difference CT value and viral load mean ratio in patients with mild and severe symptoms (p > 0.05). In conclusion, this assay with in vitro transcript RNA standard can be used to determine viral load of SARS-CoV-2. Further studies are needed to evaluate this assay with more various SARS CoV-2 in other places in Indonesia.